Electrically driven lift truck

Abstract

A lift truck has a tractive-power electric motor, an electric motor which actuates a pump for the hydraulic circuits, and batteries which supply the electric motors. In order to obtain a long working life as well as reliability and a high performance, the tractive-power motor or both motors are asynchronous and there are provided devices for sensing the angular positions and angular velocities of the motors and an electronic control unit connected to the sensor devices for controlling the power supplies to the motors in dependence on required velocities for the motors and on the basis of data provided by the sensor devices.

We claim: 
     
       1. An electrically driven lift truck comprising: (a) at least one electric motor for providing tractive power for drive wheels of the truck;   (b) an electric motor for actuating a pump which supplies hydraulic circuits of the truck;   (c) a dc power supply for supplying the electric motors, wherein the at least one electric motor for providing the tractive power or both electric motors are asynchronous motors;   (d) an angular position sensor means for measuring the angular position of the asynchronous motor;   (e) an angular speed sensor means for measuring the angular speed of the asynchronous motor; and   (f) an electronic control unit connected to the angular position sensor means and the angular speed sensor means, wherein the electronic control unit controls the power input to the asynchronous motor, the power input being dependent on required speeds of the asynchronous motor and data provided by the angular position sensor means and the angular speed sensor means.   
     
     
       2. A lift truck according to claim 1, wherein an input section of the control unit is connected to a plurality of controls of the lift truck relating to the tractive power and to the hydraulic circuits supplied by the pump and is connected to a sensor device means including said angular position sensor means and said angular speed sensor means, wherein the sensor device means provides feedback data on parameters relating to the operation of the lift truck. 
     
     
       3. A lift truck according to claim 2, wherein the control unit has a two-way connection to an instrument panel including a display and a series of indicator lights for displaying operating conditions and parameters of the lift truck as well as alarm situations, and including keys for the input of, and variation of, operating parameters shown by the display. 
     
     
       4. A lift truck according to claim 2, wherein a brake unit is provided which acts continuously on the tractive-power motor and is deactivated by the control unit on the basis of commands relating to the traction. 
     
     
       5. A lift truck according to claim 3, wherein the control unit includes a first microprocessor dedicated to the tractive-power motor, a second microprocessor dedicated to the motor for actuating the pump, a first memory which contains the programs which the microprocessors follow and the data which the microprocessors process and a second memory into which the microprocessors input data and from which they take data. 
     
     
       6. A lift truck according to claim 2, wherein the control unit controls the power supply to the motors through power stages with electronic switch bridges. 
     
     
       7. A lift truck according to claim 3, wherein sensor units are provided to sense the currents in the supply circuits to the motors and which are connected in feedback circuits to the control unit. 
     
     
       8. A lift truck according to claim 3, wherein heat probes are applied to the motors to detect their temperatures and are connected in feedback circuits to the control unit. 
     
     
       9. A lift truck according to claim 3, wherein the keys are constituted by a mode key for displaying on the display the mode "select parameter" or "modify parameter", and two selection and variation keys for selecting the parameter to be varied and for varying the parameter. 
     
     
       10. A lift truck according to claim 3, wherein the keys also control the display on the display of values of operating parameters of the lift truck as well as alarms which have occurred. 
     
     
       11. A lift truck according to claim 4, wherein the brake-unit includes two jaws which act on a drum fixed to the drive shaft of the tractive-power motor and which are actuated by a tie-rod system drawn by resilient means to effect clamping of the jaws and adapted to be slackened by hydraulic actuator means to release the jaws. 
     
     
       12. A lift truck according to claim 11, wherein the drum constitutes the annular casing of an external cooling fan of the tractive-power motor. 
     
     
       13. A lift truck according to claim 11, wherein the control unit controls the supply to the hydraulic actuator means for releasing the brake unit through a solenoid valve. 
     
     
       14. A lift truck according to claim 11, wherein means are provided for detecting whether the jaws are in their clamped or released position and are connected in feed back circuit to the control unit. 
     
     
       15. A lift truck according to claim 14, wherein the said means are constituted by a microswitch operated by the hydraulic actuator means. 
     
     
       16. A lift truck according to claim 1, wherein the asynchronous motors have squirrel cage rotors and are sealed. 
     
     
       17. A lift truck according to claim 1, wherein the devices for sensing the angular positions and angular speeds of the asynchronous motors are optical encoders. 
     
     
       18. An electrically driven lift truck comprising: (a) at least one electric motor for providing the tractive power for the drive wheels of the truck;   (b) an electric motor for actuating a pump which supplies hydraulic circuits of the truck;   (c) a dc power supply for supplying the electric motors, wherein the at least one electric motor for providing the tractive power or both electric motors are asynchronous motors;   (d) an angular position sensor means for measuring the angular position of the asynchronous motor;   (e) an angular speed sensor means for measuring the angular speed of the asynchronous motor;   (f) an electronic control unit connected to the angular position sensor means and the angular speed sensor means, wherein the electronic control unit controls the power input to the asynchronous motor with regard to the required speeds of the asynchronous motor and on the basis of data provided by the angular position sensor means and the angular speed sensor means;   (g) a plurality of controls of the lift truck connected to an input section of the electronic control unit, wherein the tractive power and the hydraulic circuits supplied by the pump are connected to a sensor device means including the angular position sensor means and the angular speed sensor means to provide feedback data on parameters relating to the operation of the lift truck;   (h) a two-way connection to an instrument panel connected to the electronic control unit, wherein the instrument panel includes: a display,   a series of indicator lights for displaying operating conditions and parameters of the lift truck as well as alarm situations,     a set of keys for the input of, and variation of, operating parameters shown by the display, wherein the set of keys include a mode key for displaying on the display a mode "select parameter" or "modify parameter", and two selection and variation keys for selecting the parameter to be varied and for varying the parameter;   (i) a first microprocessor included in the electronic control unit, wherein the first microprocessor is dedicated to the tractive-power motor;   (j) a second microprocessor included in the electronic control unit, wherein the second microprocessor is dedicated to the motor for actuating the pump;   (k) a first memory included in the electronic control unit, wherein the first memory contains the programs that the microprocessors follow and the data that the microprocessors process; and   (l) a second memory included in the electronic control unit, wherein the microprocessor inputs and retrieves data.